1. Field of the Invention
The present invention relates to an imaging apparatus, and, more particularly, to a method for mixing black and color inks in a multi-level printing system.
2. Description of the Related Art
In recent years color printers have been developed for home and office use. These printers have typically used four different inks in the colors of cyan, magenta, yellow, and black (hereinafter, CMYK). If the cyan, magenta, and yellow (hereinafter, CMY) inks are ideal, the black ink is not necessary for producing the desired color gamut. In practice, however, the black ink is required for higher quality printing since the CMY inks can not produce the desired darkness as provided by the black ink for most papers. In addition, producing the same darkness requires approximately three times the amount of ink for CMY printing than for CMYK printing. Most papers cannot sustain this much ink for dark images, which require more ink. Accordingly, the introduction of black ink in color printing is important.
Typically, in CMYK printing, each of the color inks are used in either a single high concentration, i.e., a saturated ink, or a single relatively large drop mass, which normally produce grainy images. To overcome this granularity problem in using saturated inks or large drop masses, diluted inks and/or small drop masses (small dots) have been employed. These diluted inks and/or small drop masses are used to reproduce the less intense colors of the CIELAB system, while the more intense colors require the usage of the saturated inks or large drop masses. In some printing systems, only diluted forms of the cyan and magenta inks are used. In other printing systems, a color ink may not only have both diluted and saturated inks, but may also have both small and large drop masses. In general, we call these printing systems multilevel printing systems. The number of printing levels of each primary color ink (cyan, magenta, yellow, or black) is identified by the ink concentration and drop masses available for use by the printing system. For example, a cyan ink that can be printed with diluted small dots, diluted large dots, saturated small dots, and saturated large dots will be identified as a four-printing-level primary ink used in a four-printing-level printing system.
What is needed in the art is a method of mixing black ink with color inks for use in a multi-level printing system.
The present invention provides a method of mixing black ink with color inks for use in a multi-level printing system.
The invention, in one form thereof, is directed to a method for mixing ink for use in an imaging apparatus including an ink jet printer capable of printing a plurality of primary color inks includes the steps of identifying a plurality of available printing levels for each of the plurality of primary color inks; determining a target color profile for each of the plurality of primary color inks; determining a graininess factor for each printing level of the plurality of available printing levels for each of the plurality of primary color inks; setting a mixing order for at least a portion of the plurality of available printing levels for each of the plurality of primary color inks based in part on corresponding graininess factors and at least one mixing rule; and mixing the at least a portion of the plurality of available printing levels based on the mixing order and the target color profile to generate a plurality of mixing tables, wherein one of each mixing table of the plurality of mixing tables corresponds to one of each of the plurality of primary color inks.
In another form thereof, the invention is directed to a method for mixing ink for use in an imaging apparatus, including the steps of providing a plurality of multilevel primary color inks, the plurality of multilevel primary color inks including a plurality of non-black multilevel primary color inks and a black multilevel primary color ink; determining for each multilevel primary color ink of the plurality of multilevel primary color inks a corresponding target color profile; generating for each multilevel primary color ink a corresponding mixing table based on the corresponding target color profile; mixing a black ink K with each non-black multilevel primary color ink of the plurality of non-black multilevel primary color inks using each the corresponding mixing table in mixing a plurality of CMY points in a CMY color space into a plurality of corresponding mixed CMYK points in a mixed CMYK color space wherein a process black amount in each CMY point of the plurality of CMY points is replaced, at least in part, with an amount of the black ink K for use in each corresponding mixed CMYK point of the plurality of corresponding mixed CMYK points; and optimizing a total amount of the black ink K used in the mixing step, wherein the process black amount is an amount of black color in each of the plurality of CMY points that exists without the use of black ink.
An advantage of the present invention is the ability to mix black ink into a CMY color space to produce a mixed CMYK color space using primary color inks that can be printed with more than one printing level, resulting in a printing method that uses less ink and results in less bleed through in the recording medium than the use of conventional color spaces.
Another advantage is the ability to produce a mixed CMYK color gamut for a multi-level printing system that is larger than conventional color gamuts, allowing better matching of RGB colors with printed output.